Worried about IBC

Hi all, I am 37 year old Asian mom of 2 young kids. 10 months back I felt my left breast was lumpy and got mammogram and ultrasound done. They said it was dense breast tissue. Last month, I found a lump / thickening in my left breast under the nipple. It's round. I feel it changes shape for example when I touch, it gets harder. In the shower it gets harder. The skin around has turned black. The protrusion is clearly visible. I have irritation and sore breasts. The pain was worst before I had periods. I felt the area was more swollen before periods. After periods I felt better in terms of irritation/ soreness. I felt like the lump reduced in size. 2 weeks after periods again I started feeling discomfort and went to my gynac. He ordered mammogram, ultrasound and biopsy. He didn't seem encouraging. I read about IBC and I feel like I have most of the symptoms. I am freaking out. I got appointment for tests on Thursday. Could this be anything else ? I read that if it was other forms of cancer it would have shown up in my ultrasound 10 months back. IBC is only one that grows this fast. The wait is killing me.